The Transformers star, 34, wore a midriff-baring crop top, a black jacket and jeans for the outing, while Kelly, 30, was dressed in all black with his hair in pigtails.
Lavigne, 36, donned a black sweatshirt from her Abbey Dawn clothing line and leather pants, while her rapper boyfriend, 33, had a neon-green mohawk and a face mask promoting his latest album, Internet Killed the Rockstar.
Us Weekly confirmed last month that the “Complicated” singer was dating Mod Sun after they worked together on the song “Flames.”
Mod Sun, whose real name is Derek Ryan Smith, previously raved about the “Sk8er Boi” singer in January, after their collaboration on “Flames.”
“Avril Lavigne has one of my favorite voices in music,” he said, according to Entertainment Tonight Canada. “It’s so strong and confident, yet filled with emotion and one-of-a-kind inflections that only her voice can do.”
“This song holds a lot more weight than meets the eye. There’s a very deep message within it,” he added.
“He’s an incredible artist and producer,” she continued, saying that their single “is the first of many.”
Lavigne teased a collaboration with MGK and Mod Sun at the end of December, posting photos on Instagram of the trio working together in the studio. “So are we ready for new music in the new year or what? Lemme know…..” she captioned the pics. The Grammy nominee is currently working on the follow-up to her 2019 album, Head Above Water.
Kelly and Fox, meanwhile, met on the set of their upcoming film, Midnight in the Switchgrass. Us Weekly revealed in June 2020 that the pair were “officially dating” one month after her husband, Brian Austin Green, confirmed their split after nearly 10 years together. The pair share three sons, Noah, 8, Bodhi, 7, and Journey, 4. The Beverly Hills, 90210 alum filed for divorce in November.
A source told Us in February that the “Bloody Valentine” singer is “super into” Fox and thinks he is “the luckiest guy in the world.”
“MGK thinks Megan is different than the other A-listers he’s dated,” a source told Us exclusively. “He thinks she is a total bombshell in every way and basically worships the ground she walks on.”
While the pair denied engagement rumors in January, the insider added that Kelly, whose real name is Richard Colson Baker, “would marry her in a heartbeat,” but Fox “isn’t in any rush to get married again right now.”
Scroll down to see pics from their double date.